Cast one-piece annular rim member for a vehicle wheel

ABSTRACT

In a mold for casting an annular rim member for use in a vehicle wheel for mounting a pneumatic tire, the mold cavity is formed so that the casting has at least one of a radial overdimension or a radial underdimension and its outer surface which faces the tire has an unsegmented annular area. After the casting is solidified and removed from the mold, it is plastically deformed by radially directed cold forming or working to remove the radial overdimension or underdimension. An iron-carbon melt is used for the casting to provide a ductile structure whose yield point is exceeded in carrying out the plastic deformation.

SUMMARY OF THE INVENTION

The invention relates to the formation of a cast one-piece annular rimmember for a vehicle wheel used for mounting a pneumatic tire, inparticular a tubeless tire, and more particularly, it concerns thecasting of the rim member from iron-carbon melt within a mold so thatfollowing the casting the rim member has at least one of a radialoverdimension or underdimension which is subsequently removed by plasticdeformation.

At the present time, rims for passenger and motor vehicle wheelsequipped with pneumatic tires are generally formed of sheet iron. Arolled sheet strip of suitable dimensions is bent into a ring and weldedtogether at its ends. After the welding seam is smoothened, the rimsection is continuously rolled in several stages until it reaches itsfinal shape by means of a plurality of compression cycles effected inthe radial direction as well as in the axial direction. The workingperformed in the radial direction can be either by expanding orupsetting. Next the rim section is joined, generally by welding, with awheel lip to form a disk or center-web wheel or, in the alternative, therim is provided with a support ring for its assembly upon a spokeelement or wheelspider.

The manufacturing procedure described above in a greatly simplified forminvolves a large number of individual operations. It requiresappropriately specialized complex manufacturing facilities which requireheavy investment, expensive maintenance and continuous supervision.Shaping by means of rolls and rollers provides a relatively narrowlatitude with regard to the profile of the rim and it is difficult tomeet the tolerances required for the diameter dimensions, concentricityand the like. The welding operations result in local structural changesand in a weakening of the material, and internal stresses developedcause distortions of the workpiece. Finally, sheet metal rims are alsorelatively corrosion-prone.

It has also been proposed to cast rims with a wheel dish or a supportring so that the rim member is shaped directly as a casting in a processusing light metals, cast iron, or steel. When rims are cast in thismanner it is necessary, with regard to the surface property, projectingcasting burrs, and dimensional deviations of the raw casting, to machinethe outwardly facing surface of the rim to provide a satisfactoryseating for the tire. Extensive and accurate machining of the riminvolves considerable costs and presupposes corresponding processingallowances with regard to the rim. It is particularly disadvantageousthat, as a result of out-of-round or eccentricity frequently present inthe casting, the material is removed unevenly during machining,producing a non-uniform wall thickness over the circumference of therim. As a result, substantial imbalances as well as differentialdeflections under load develop in the rim. These characteristics haveseriously impeded the extensive use of casting in the manufacture ofwheel rims.

It is a primary object of the present invention to obviate the problemsexperienced in the past and to provide an economical process for themanufacture of high quality cast annular rims and annular components forsegmented annular rims.

Therefore, in accordance with the present invention, the rim or rimcomponent is provided at least along a portion of the rim cross-section,with a radial overdimension and/or underdimension and its outer surfacewhich faces the tire is molded as an unsegmented annular surface.Further, an ironcarbon melt is used in casting the rim member so that ithas a ductile character. After the casting has solidified, it isradially plastically deformed by cold forming or working to provide therim member with its finished dimensions. There are two preferredvariations in the materials used for casting the rim member, oneutilizes a cast iron melt pretreated for nodular or spheroidal graphiteprecipitation and the other uses a cast steel melt which, following thestandard heat treatment of the casting, results in a ductile structuresuitable for subsequent plastic working.

It should be emphasized, in the present invention, that the term "radialoverdimension" does not indicate the customary excess dimension providedfor shrinkage upon the solidification of a casting nor is it aprocessing allowance as required under other circumstances, rather thediameter of the raw casting is enlarged to such an extent that, uponupsetting to the finished dimension, the yield point and the compressiveyield point of the mineral are exceeded. Similarly, the term "radialunderdimension" indicates a diameter of the casting in which, upon beingexpanded to the finished dimension, the yield point of the material isexceeded.

In addition, the invention relates to an annular rim or an annular rimcomponent formed in accordance with the abovementioned process, which ischaracterized by the fact that its outer surface arranged to face thetire, is constituted by an intact skin.

The process of the present invention for forming an annular rim memberaffords a very economical process making use of all the advantages ofcasting, such as greater freedom in shaping, permitting even deviationsfrom a true rotary body, one-piece manufacture of the rim and wheel lipor supporting ring or supporting lugs in the same operating cycle, themanufacture of different types of workpieces in the same facility,simple conversion of models and the like. Compared to the castingprocesses used in the past, the costly and timeconsuming machining ofthe outer surface of the casting can be eliminated which is achieved onone hand by forming an unsegmented annular area on the outer surface ofthe casting which does not result in any burrs or ribs and, on the otherhand, by bringing the wheel member to the finished dimensions by plasticdeformation through cold working or forming. The radial upsetting and/orexpanding of the rim member results in reinforcing the ductile castingmaterial and in the creation of inherent compressive or tensile stressesacting as desirable prestresses with respect to the load to be carriedby the wheel. The rims formed in accordance with the present inventionare characterized by a narrow, circumferentially uniform wall thickness.Owing to the intact condition of the skin, the rim members are moreresistant to corrosion than sheet metal or cast and machined rims.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there are illustrated and described preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a block diagram showing the steps involved in the formation ofa rim member in accordance with the present invention;

FIG. 2 is a vertical sectional view taken along the axis of a rim membershowing a mold for forming the rim member and a wheel lip;

FIG. 3 is a half-view of a disk or center-web wheel cast in the moldshown in FIG. 2;

FIG. 4 is a half-view, similar to FIG. 3, however showing a cast rimprovided with a supporting ring or support lugs;

FIG. 5 is a cross-sectional view taken along line V--V in FIG. 3;

FIG. 6 is a cross-sectional view taken along line VI--VI of FIG. 4;

FIGS. 7, 8 and 9 illustrate a device for radially upsetting a cast rim,with each figure illustrating a different phase of the formingoperation;

FIG. 10 is a vertical sectional view through a mold similar to thatshown in FIG. 2, however, indicating the formation of an annular rimmember segmented transversely of its central axis and with the rimincluding a supporting ring; and

FIG. 11 is a cross-sectional view through an annular rim similar to thatshown in FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

Prior to a detailed discussion of the various phases of the processembodying the present invention, FIG. 1 diagrammatically illustrates theessential interrelated phases A to D of one embodiment of the process.In the embodiment illustrated in FIG. 1 a cast iron melt is used whichhas been pretreated for spheroidal or nodular graphite precipitation.

In FIG. 1 the block A refers to the manufacture of the mold. Preferably,a standard, one-time mold is used, for instance a sand mold with orwithout a molding box, two examples of which are illustrated in FIGS. 2and 10. The cast iron melt charged into the mold is suitably pretreated,as indicated by block B, in accordance with a known process, forinstance, magnesium treatment, so that following pouring of the mold,block C, and upon solidification, the carbon will precipitatepredominantly as spheroidal graphite and a ductile casting will beformed.

Following the solidification of the casting, various operations takeplace which have not been illustrated in any detail, such as removalfrom the mold, deflashing, separation from the casting system, anddeburring. In the final block D, the cast rim member is plasticallydeformed by cold working or forming and during this operation the rimmember cast with a radial overdimension and/or a radial underdimensionis brought to its finished dimension by radially upsetting or expanding,as required. This part of the formation of the rim member is describedin greater detail with regard to FIGS. 7 - 9 and also with respect toFIGS. 5, 6 and 11. The portion of the operation characterized by block Dessentially completes the shaping of the rim or rim component, all thatremains is the machining of the assembly flange on the wheel lip and thedrilling of assembly holes, and to complete the machining of thesupporting lugs or of the support.

One variation of the process as described by FIG. 1 is the selection ofthe material used as a cast wheel melt in place of a cast iron melt.Such a variation eliminates the pretreatment of the melt, block B,however, it is as a rule necessary to subject the solidified steelcastings to a known heat treatment for converting the solidificationpattern of the casting into a fine-grain secondary structure providedwith the ductility required for subsequent cold working. However, aprocess using such a variation on the materials employed is identicalwith regard to phases A, C and D.

The important considerations regarding the manufacture of the mold arediscussed below with reference to FIG. 2. In FIG. 2 a sand mold is shownin cross-section and consists of a lower mold section 1, an upper moldsection 2, and a preferably hollow annular core 3 bridging the locationof the mold partition 4 between the two mold sections. As a result, theinner surface of the core 3 defines the radially outer surface 19 of thecasting. The upper mold section 2 includes an upper duct 5 leading to acasting system 6. Within the mold, recesses form a mold cavity 8 towhich feeder ducts 7 are connected. The mold in FIG. 2 forms a disk orcenter-web wheel as illustrated in FIGS. 3 and 5 and includes an annularone-piece flat-shouldered drop-center rim 11 and a wheel lip or dish 12.The wheel lip 12 has openings 13 and recesses 15 are formed in theflange 14 adjoining the wheel lip, both the openings 13 and the recesses15 are formed during the molding operation, however, the bore holes 16provided in the flange for assembly purposes, are drilled in the castingpreferably subsequent to the operating cycle described above. In FIGS. 4and 6, a rim 20 is formed having a rim portion identical with that shownin FIGS. 3 and 5. However, the rim 20 is assembled on a spoke element orwheelspider and, for this purpose, is provided with a plurality ofsupporting lugs 21. In place of the supporting lugs, a known continuoussupport ring 22 can be provided as indicated by the dash-dot line inFIGS. 4 and 6. It is essential in molding the rims or rim portions, inaccordance with the present invention, that the outer surface 19 of therim, note FIGS. 2, 5 and 6, which faces the tire is formed as anunsegmented annular area to prevent any shifting or the formation of anytransverse burrs. In the mold shown in FIG. 2, the unsegmented annulararea is provided by the one-piece, closed annular core 3. In the mold,shown in FIG. 2, at most peripherally-oriented burrs are located at therim edges outside the tire seating area, that is, the location 9 in FIG.2, and such burrs can be easily removed, such as by trimming.

Moreover, with respect to the subsequent plastic deformation of the rim,it is provided with a radial overdimension exceeding that customarilyprovided for shrinkage which occurs during solidification or for theallowance provided for processing purposes which would not be requiredin the present instance. To illustrate the radial overdimension, the rimcontour of the solidified casting is shown in FIGS. 5 and 6 as adash-and-dot line and the contour of the finished, radially upset andplastically deformed rim is shown in full lines. The radii at the rimedges 18 are shown by R1 in the as cast state of the rim and by R2 afterthe finishing operation has been completed on the rim. The overdimensionat the rim edge 18 and the subsequent reduction under plasticdeformation can be advantageously selected to be greater than theoverdimension at the rim base where the rim proceeds to form the wheellip 12 or the supporting lugs 21 for support ring 22. The amount of theoverdimension is such that, upon cold working of the ductile castmaterial, the yield point of the material is clearly exceeded.Accordingly, the amount of the overdimension at the rim edge is selectedin the range between 1 and 10%, preferable approximately 1.5 to 2%, ofthe diametral dimensions. Measurements performed on a 22.5 inchdrop-center, (rated diameter 571.5mm), in accordance with FIGS. 5 or 6,and made of nodular or spheroidal graphite cast iron grade GGG-42 showthe diameter difference to constitute 10mm at the edge of the rim and6mm at the base of the rim. Similar values are applicable when caststeel is used in forming the rim.

A material which is highly suitable for the above process is cast ironwith nodular graphite. Preferably, a cast iron melt can be pretreated bymeans of metallic magnesium in a process described in the publication"Giesserei" (59), vol. 1 dated Jan. 13, 1972, pages 1-12. A meltpretreated in this manner and containing, for instance, 3.6-3.8% C andabout 2.4% Si, after pretreatment will yield a ductile, ferriticstructure accompanied by predominantly nodular cast iron precipitation.

The material data corresponds to class GGG-42 according to DIN (GermanIndustrial Standards) 1693 (tensile strength minimum 42 kilopond/sq.mm,yield point minimum 28 kilopond/sq.mm., elongation minimum 12%, Grinellhardness 140-190).

A suitable cast steel for use in the process is GS-45.3 according toDIN, that is, a steel melt containing approximately 0.21% C, 017% Mn,and 0.4% Si which produces, following standard heat treatment (annealingat 900°-1000°C), a casting having a ductile structure and the followingminimum characteristics: tensile strength 45 kiloponds/ sq. mm., yieldpoint point 23 kiloponds/ sq. mm, elongation 22%, Brinell hardness125-165. Such castings, having wall thicknesses of about 7-8mm in thearea of the rim profile, with respect to the above described example,can in an excellent manner be plastically deformed by cold working asrequired.

The cold working of the rim members cast in the manner described aboveis explained below with reference to FIGS. 7-9. In FIGS. 7-9 disk orcenter-web wheels 10 are shown, such as are illustrated in FIGS. 3 and5, however, it would also be possible to use the rims of FIGS. 4 and 6in the forming apparatus shown in FIGS. 7-9. The wheels 10 are advancedin a step-wise fashion along continuous rails 30 of a processing linefor movement into the working device illustrated in FIGS. 7-9. In theseFigures a workpiece 10' is shown in position for movement into theworking device. Within the forming or working device, lifting rods 31are positioned between the rails 30 and can be raised and lowered eitherpneumatically or by other means. At their upper ends, the rods 31 havehorizontally arranged crossbars 32 which can be lowered into recesses 33in the rails so that the upper surfaces of the crossbars are flush withthe top of the rails. In the retracted or lowered position of thelifting rods 31, the workpiece 10' can be pushed forwardly onto thecrossbars 32. Subsequently, the rim or workpiece 10 can be raised bymeans of the lifting rods 31 into the position shown in the upperportion of FIG. 7.

The device shown in FIGS. 7-9 is similar to known devices for shapingannular sheet metal components. A solid guide ring 36 is supported oncolumns 35 from a base 34 and the interior of the ring includes aplurality of plane, sloping guide areas 37, that is the guide areasslope inwardly in the upward direction. Die segments 40 provided with adie surface adapted to the respective workpiece can be moved along thesloping guide areas 37. The die segments 40 are positioned on the ring39 which rests on the pistons or plungers of a plurality of hydraulichoisting units 38 extending about the circumference of the ring 39 andsupported at their lower ends by the base 34.

In the lower limiting position of the ring 39 and the segments 40, thesegments have a maximum radial dimension with respect to the centralaxis of the device. As indicated above, the rim workpiece 10 is liftedby the lifting rods 31 into the open ring of segments 40. Subsequently,the ring 39 is raised by the hydraulic units 38 and, at the same time,the rim workpiece is lifted by the rods 31. During such upward movement,the segments move along the inwardly sloping guide areas 37 and radiallyapproach the outer surfaces of the rim workpiece 10. FIG. 8 illustratesthe lifting positions in which the die segments are flush against therim edges. Since the radial overdimension of the cast rims is less atthe base 17 of the rim than at its edge 18, as explained with regard tothe arrangement shown in FIGS. 5 and 6, a certain spacing exists in theposition shown in FIG. 8 between the rim base and the correspondingsurface of the segments 40 designed to provide the finished rim profile.As the ring 39 and the segments continue to be displaced upwardly theyreach the position shown in FIG. 9 and provide a complete closing of thecollar of segments with a radial compression or calibrating of the rimto obtain plastic deformation by cold working.

After the rim has achieved its final or finished shape, the ring 39supporting the segments 40 is lowered, by releasing the liftingapparatus 38, into the position illustrated in FIG. 7 with the collar ofthe segments opening up. At the same time, the finished rim workpiece 10is lowered and deposited on the rails 30 by means of the lifting rods31. The completed workpiece is then moved out of the device and the nextworkpiece is positioned to commence the shaping cycle.

In FIGS. 10 and 11 another embodiment is shown of a steep-shoulderedannular rim segmented in a plane extending transversely through thecentral axis of the rim. The mold shown in FIG. 10 forms a closedannular rim member 50, note FIG. 11, having one rim lobe 52 and a rotarythrust ring 53 having an inwardly tapering surface, so that followingthe mounting of the tire, a second annular rim lobe 51 can be secured tothe thrust ring by bolts. A rim assembled in this manner is intended tobe mounted on a wheelspider 54 by means of clamps 55 both of which areindicated by dot-dash lines in FIG. 11.

FIG. 10 illustrates a vertical section through a casting mold, such as aone-time sand mold, for forming the rim part or member 50 shown in FIG.11. The mold consists of a lower portion 41 and an upper portion 42having a parting surface or joint 44 between them. The upper and lowerportions 41, 42 of the mold form a mold cavity 48. An upper duct 45 isconnected by a casting system 46 to a feeder duct 47 connected to themold cavity 48 for filling the mold cavity with the melt. Unlike theunsegmented rim disclosed in FIGS. 3-6, the rim part shown in FIG. 11can be molded without an annular core. The joint area 44 of the mold, asshown in FIG. 10, has been arranged so that the outer surface 49 of therim part 50 which faces the tire, is molded as an unsegmented annulararea.

In FIG. 11 the profile of the casting, as initially formed, is shown indot-dash line while the outline of the finished rim part 50 is shown infull line. Further, the portion of the cross-section of the rim part 50is shown on the righthand part of FIG. 11 and including the rim lobe 52is formed with a radial overdimension. The extent of this radialoverdimension, that is, the differences in the radii R1-R2 isestablished by taking into account the ductile casting material used andthe other considerations used regarding the previous example. Withregard to the die used in providing the finished dimensions of the rimpart 50, it may be appropriate to form the portion 56 of the rim part,that is as shown in the lefthand part of FIG. 11, so that it is radiallyunderdimensioned. That portion of the rim part 50 which is radiallyoverdimensioned is cold worked to attain the desired plastic deformationand its final dimensions are achieved by radial upsetting in a devicesimilar to that shown in FIGS. 7-9. However, with regard to the radiallyunderdimensioned portion 56, which is not significant as far as theseating of the tire is concerned, it is necessary to expand the rim partto reach the final dimension. This operation can be performed at thesame time as the radial upsetting by a known expander device, not shown,of the type manufactured by Grotnes Machine Work, Inc. of Chicago,Illinois.

Moreover, in the case of certain rim designs it may be appropriate tocast the entire rim so that it is radially underdimensioned and toexpand it to the desired final dimensions. The above-mentioned expanderdevice would be suitable for this purpose.

The ductile casting materials used for the previously describedembodiments are also appropriate for the annular rim part 50 of FIG. 11and, therefore, have not been repeated.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

I claim:
 1. Process for the manufacture of an annular rim member toestablished radial dimensions for use in a vehicle wheel equipped with apneumatic tire and, in particular, a tubeless tire, with the rim memberforming a one-piece annular rim or an annular rim part including a wheellip, supporting lugs or a support ring, comprising the steps of forminga mold cavity for the rim member with at least one of a radialoverdimension and a radial underdimension of an amount other than thecustomary excess dimension provided for shrinkage or as a processingallowance, at least over an annular portion of the rim cross-section andwith the outer surface of the rim member arranged to face the tirehaving an unitary annular area, pouring an iron-carbon melt into themold cavity for forming the rim member with a ductile structure,removing the cast rim member from the mold cavity and radially plasticcold working the solidified cast rim member for plastically deformingthe rim member during which plastic deformation the yield point of thecast ductile structure is exceeded and attain the established radialdimensions of the rim member for removing the at least one of a radialoverdimension and a radial underdimension.
 2. Process for themanufacture of an annular rim member, as set forth in claim 1, includingthe step of forming the surface of the mold cavity which defines theouter area of the rim member facing the tire with a unitary closedannular core.
 3. Process for the manufacture of an annular rim member,as set forth in claim 1, including the step of forming the cast rimmember with at least one of a radial overdimension and a radialunderdimension which is greater at the edges of the rim member than atthe base of the rim member spaced inwardly from the rim edge.
 4. Processfor the manufacture of an annular rim member, as set forth in claim 1,including the step of limiting the radial overdimension and/orunderdimension of the cast rim member to the range of 1 to 10% of thediameter dimensions of the rim member.
 5. Process for the manufacture ofan annular rim member, as set forth in claim 4, comprising limiting theradial overdimension and/or radial underdimension of the cast rim memberto the range of 1.5 to 2% of the diameter dimensions of the rim member.6. Process for the manufacture of an annular rim member, as set forth inclaim 1, wherein an annular portion of the rim is radiallyoverdimensioned and another annular portion of the rim is radiallyunderdimensioned and plastically deforming the rim member by upsettingthe radially overdimensioned annular portion and expanding the radiallyunderdimensioned annular portion to achieve the established radialdimensions of the rim member.
 7. Process for the manufacture of anannular rim member, as set forth in claim 1, including the step ofpretreating the iron-carbon melt for spheroidal graphite precipitationprior to pouring it into the mold cavity.
 8. Process for the manufactureof an annular rim member, as set forth in claim 1, including the step ofpouring a cast steel melt as the iron-carbon melt into the mold cavity.